docs: add contributing guide.

CONTRIBUTING.md

@@ -0,0 +1,100 @@
+Contributing Guide
+===
+
+Any contributions are welcomed:
+
+- Source code.
+- Documentation improvements.
+- Bug reports and code reviews.
+
+How to Contribute Source Code
+---
+
+1. Check for [open issues](https://github.com/jayvynl/django-clickhouse-backend/issues) or open a fresh issue to start a discussion around a feature idea or a bug.
+2. Fork the repository on GitHub and make your changes. 
+3. Write some unit tests which shows that the bug was fixed or the feature works as expected.
+4. Send a pull request, the PR must pass code review and GitHub workflow before merging.
+
+### Setup Development Environment
+
+*This step is optional.*
+
+1. Clone the forked repository and cd into it.
+
+2. Install [tox](https://tox.wiki/).
+   ```shell
+   pip install tox
+   ```
+
+3. Start ClickHouse cluster.
+   Docker and docker compose are required.
+   ```shell
+   docker compose up -d
+   ```
+
+4. Install dependencies.
+   ```shell
+   pip install -e .
+   ```
+
+### Code Style
+
+This project use:
+
+- [isort](https://github.com/PyCQA/isort#readme) to automate import sorting.
+- [black](https://black.readthedocs.io/en/stable/) to format code.
+- [flake8](https://pypi.org/project/flake8/) to lint code.
+
+If tox is installed, code formatting can be run as:
+
+```shell
+tox -e format
+```
+
+code linting can be run as:
+
+```shell
+tox -e lint
+```
+
+### Code Conventions
+
+As a Django derivative project, code conventions should follow Django source code whenever possible, including but not limited to:
+
+1. Code directories arrangement.
+2. Variable names.
+3. Feature implementation.
+
+For example:
+
+- Non-aggregation SQL functions are placed in `clickhouse_backend/models/functions`, because Django place them in `django/db/models/functions`.
+- Fields should be named as XXXField instead XXXType or XXXColumn.
+- Index implementation should refer to Django index, not a completely new one.
+
+### Unit Tests
+
+Any bug fix or feature implementation must be followed by some tests. This project use [Django test suite](https://docs.djangoproject.com/en/4.2/topics/testing/) for tests.
+
+Run tests:
+
+```shell
+python tests/runtests.py
+```
+
+If tox is installed, a list of default environments can be seen as follows:
+
+```shell
+tox -l
+```
+
+Run test for specific Python version and Django version:
+
+```shell
+tox -e py3.9-django3.2
+```
+
+run test for all supported Python version and Django version:
+
+```shell
+tox
+```

README.md

@@ -584,6 +584,10 @@ Changelog
 
 [All changelogs](https://github.com/jayvynl/django-clickhouse-backend/blob/main/CHANGELOG.md).
 
+Contributing
+---
+
+Read [Contributing guide](./CONTRIBUTING.md).
 
 License
 ---